1. Field of the Invention
The present invention relates to an image forming system and an image forming apparatus constituting the system.
2. Related Background Art
An ink jet recording apparatus using a printing means for an ink jet scheme to record information on an elongated recording medium such as a cloth is a relatively new recording apparatus.
A recording apparatus for printing information on a cloth is known as a cloth printing apparatus. Main conventional printing methods are:
A) roller printing for pressing a roller engraved with a pattern against a cloth to form a continuous pattern; and PA1 B) screen printing for preparing screen plates, the number of which is equal to the number of colors to be stacked. PA1 1) Image densities to be reproduced on cloths using identical amounts of ink vary depending on types of cloths. PA1 2) When recording is performed in a constant cloth feed quantity, serial stripes appear differently between scanning cycles of a recording head. This may occur due to elongation properties of cloths. PA1 3) The discharge port surface of the recording head is interfered with fluffs. A gap between the cloth surface and the discharge port surface must be increased for a fiber having large fluffs, such as wool. In this case, the offset influence of a discharge direction as one of the discharge characteristics of a recording head typically occurs, and density variations occurs. PA1 4) The cloth printing apparatus is a manufacturing equipment which is much larger than a printer and a copy machine as the applications of the conventional ink jet scheme. PA1 5) In arranging a cloth printing apparatus, a host computer such as a workstation generates and manages printing image data. A plurality of cloth printing apparatuses are preferably managed by one host computer through a network. Maintenance personnel can preferably obtain necessary information on an operation unit serving as an operation input/output means of the cloth printing apparatus and enter necessary instructions. PA1 6) A cloth printing apparatus generally produces dry goods in continuous output of 50 m or more. In this case, when printing up to 40 m is completed, and abnormal printing occurs, this dry-goods item does not have any commercial value. The portion up to 40 m is undesirably wasted, resulting in a great loss. PA1 (1) When the same data is printed at the same position a plurality of times to increase the printing density, the printing time is undesirably doubled. PA1 (2) A scanning rate of a printing head may be increased to obtain a higher printing speed during thinned printing. However, assume that a predetermined period of time required for performing printing by one normal scanning cycle is defined as "1". If the printing speed is doubled and printing is performed by two printing cycles in accordance with thinned printing, the predetermined period of time is about "1.5" times. When the scanning rate is doubled to perform printing by four scanning cycles, the predetermined period of time becomes about "3" times.
The advantages and disadvantages of these conventional methods and an ink jet cloth printing method will not be described in detail herein. The ink jet cloth printing method has received a great deal of attention in view of proposal of a new design environment and innovation of a printing work site in consideration of environmental countermeasures.
A known ink jet scheme is used in a recording apparatus such as a printer or copying machine using a recording medium (e.g., paper). This ink jet recording apparatus is applied to a printing apparatus using a cloth as a recording medium in place of paper, new technical problems are posed. For example, various kinds of cloths used in printing, such as natural fibers (e.g., cotton, silk, and wool) and synthetic fibers (e.g., Nylon, polyester, and acrylic). Characteristic differences between these fibers are described in detail in, e.g., "Senshoku", ed., Kazuo Kondo, published from Tokyo Denki Daikaku Shuppan-Kyoku.
The detailed problems will be described below.
For example, the width of a cloth subjected to printing per scanning cycle is about 2 m, and a memory capacity for a circuit system is very large. In addition, an image memory for storing original image data is as large as several 100 Mbytes. Although the number of ink colors in a copy machine or the like is four, i.e., cyan, magenta, yellow, and black, the cloth printing apparatus requires two or more colors in the form of special or specific colors in addition to the above four colors. To perform maintenance of such an apparatus, maintenance personnel must have higher technical levels, and maintenance time may be undesirably prolonged.
In an ink jet printer for recording an image using a recording head having a plurality of nozzles, the recording heads each having the plurality of nozzles are scanned to record image data common to all the recording heads on a recording medium, thereby preventing image variations caused by the nozzle characteristics of the recording heads. This recording scheme is called multi-scanning.
The following problems are posed by the conventional multi-scanning printing method.
The printing speed is greatly reduced if printing data is thinned and printed to increase the printing density.
In a conventional image output apparatus such as a color printer, color image data received from an image supply apparatus such as a host computer is often expressed as a combination (R, G, and B) of red (R), green (G), and blue (B) as the additive primaries. In particular, when the image supply apparatus is a computer, digital signals representing the quantized intensities of the R, G, and B components are often input because a color image is expressed in the form of R, G, and B luminance data in consideration of matching with a color monitor of the computer.
Cyan (C), magenta (M), and yellow (Y) as complementary colors of R, G, and B are often used as the colors of recording agents or colorants (e.g., a color toner and a color ink) for forming an image in an image output apparatus (a black (BK) recording agent may also be used). C, M and Y are the subtractive primaries.
In this case, the image output apparatus converts the input signals (R, G, and B) into density data C, M, Y, and (K) and controls the amounts of color agents in accordance with these density data, thereby forming an image.
In an image output apparatus, a recording agent having a color (e.g., a metallic color; to be referred to as a special or specific color hereinafter), except for C, M, Y, and BK, as a recording agent for forming an image may be expected to be used. The special color is used when a color which cannot be expressed by C, M, Y, and BK is required in an output image (in particular, in the field of cloth printing, this applies to a case in which a strong demand arises for faithfully reproducing a design designed by a designer) or when an amount of color development agent such as an ink or toner is kept small.
A conventional image forming system is incompatible with use of a color development material of a special color due to its capability.
For example, a conventional image output apparatus cannot convert R, G, and B components of the input image data into density data including a special color. In addition, no color development material corresponding to the special color is available, and an output image including the special color cannot be obtained.
There are many problems left unsolved as to how a special color is designated, and how special color application modes such as a color range to be substituted for the special color and a special color application region are designated.
An image supply apparatus H may supply C, M, Y, and BK as the signal components used in an image output apparatus. In this case, the image supply apparatus must perform processing for color-separating image data into C, M, Y, and BK in accordance with the characteristics of the image output apparatus and supplying the color-separated components to the image output apparatus. In this case, a conventional image supply apparatus cannot color-separates image data into C, M, Y, and BK, and then special colors. Even if this color separation is possible, such color-separated data cannot be accepted by the image output apparatus.
In some conventional image forming systems of this type, an image supply apparatus such as a host computer transmits color image data for recording, and an image output apparatus receives these data to perform color image formation using recording agents of cyan (C), magenta (M), yellow (Y), and black (BK).
In image recording on a recording medium using this image forming system, it is important to determine whether a recorded image faithfully reproduces the original colors.
For example, in the field of cloth printing for printing images on cloths, a designer designs an original image while selecting colors from standard color patches. Color reproducibility at the time of printing for the selected colors greatly depends on reproducibility of a cloth printing system. Strong demand therefore has arisen for faithfully reproducing the selected colors.